DESCRIPTION (from abstract): Serotonin (5-HT) may participate in the pathogenesis of pulmonary hypertension where smooth muscle cell (SMC) hyperplasia and hypertrophy occur. The principle investigator has found that 5-HT stimulates both hyperplasia and hypertrophy of bovine pulmonary artery SMCs in culture. Preliminary observations indicate that intracellular signalin for growth occurs through action of a 5-HT transporter in these cells and is closely linked to protein tyrosine phosphorylation and production of superoxide. Enhanced phosphorylation of GTPase-activating protein (GAP) is one of the events that accompanies the stimulatory process. Furthermore, 5-HT-induced growth of these cells is blocked by anti-oxidants and inhibition of tyrosine kinase or p21 Ras. Based on these and other results the investigators postulate that 5-HT transport initiates a cellular proliferative and hypertrophic response via superoxide formation and a protein phosphorylation cascade that involves GAP, p21 Ras, Raf-1, and MAP kinases. Th STAT transcription pathway may also be involved. Specific aim 1 will further explore the effect of 5-HT on the protein phosphorylation signaling cascade of SMCs examining the MAP kinase cascade outlined above using techniques similar to those previously used for GAP. Activation of the transcription factors AP-1 NFkB, and STAT by 5-HT will also be assessed and it will be determined if this occurs thorough superoxide formation. Specific aim 2 will further evaluate superoxide as an intermediate signal in SMC growth and will explore the relationship of p21 Ras and MAPK activations in superoxide formation. Specific aim 3 will evaluate the influence of 5-HT on a limited number of other cells known to contain either 5-HT transporter or the 5-HT receptor to determine if unifying signaling and downstream effector pathways for cellular growth induce by 5-HT can be identified. Specific aim 4 will determine if the cyclic nucleotides, cAMP and cGMP, cause inhibition of SMC growth through inhibition of the protein phosphorylation cascade or formation of superoxide. Specific ai 5 will utilize PCR methodology to determine if stimulation of 5-HT uptake by hypoxia occurs through enhancement of transcription of the 5-HT transporter an will determine if SMCs pre-exposed to hypoxia demonstrate enhancement of 5-HT-induced signaling pathways that lead to SMC hyperplasia and hypertrophy.